Connected: An Internet Encyclopedia
RFC 1034 - 6.2.1. QNAME=SRI-NIC.ARPA, QTYPE=A

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### 6.2.1. QNAME=SRI-NIC.ARPA, QTYPE=A

The query would look like:

                   +---------------------------------------------------+
        Header     | OPCODE=SQUERY                                     |
                   +---------------------------------------------------+
        Question   | QNAME=SRI-NIC.ARPA., QCLASS=IN, QTYPE=A           |
                   +---------------------------------------------------+
        Answer     | <empty>                                           |
                   +---------------------------------------------------+
        Authority  | <empty>                                           |
                   +---------------------------------------------------+
        Additional | <empty>                                           |
                   +---------------------------------------------------+

The response from C.ISI.EDU would be:

                   +---------------------------------------------------+
        Header     | OPCODE=SQUERY, RESPONSE, AA                       |
                   +---------------------------------------------------+
        Question   | QNAME=SRI-NIC.ARPA., QCLASS=IN, QTYPE=A           |
                   +---------------------------------------------------+
        Answer     | SRI-NIC.ARPA. 86400 IN A 26.0.0.73                |
                   |               86400 IN A 10.0.0.51                |
                   +---------------------------------------------------+
        Authority  | <empty>                                           |
                   +---------------------------------------------------+
        Additional | <empty>                                           |
                   +---------------------------------------------------+

The header of the response looks like the header of the query, except that the RESPONSE bit is set, indicating that this message is a response, not a query, and the Authoritative Answer (AA) bit is set indicating that the address RRs in the answer section are from authoritative data. The question section of the response matches the question section of the query.

If the same query was sent to some other server which was not authoritative for SRI-NIC.ARPA, the response might be:

                   +---------------------------------------------------+
        Header     | OPCODE=SQUERY,RESPONSE                            |
                   +---------------------------------------------------+
        Question   | QNAME=SRI-NIC.ARPA., QCLASS=IN, QTYPE=A           |
                   +---------------------------------------------------+
        Answer     | SRI-NIC.ARPA. 1777 IN A 10.0.0.51                 |
                   |               1777 IN A 26.0.0.73                 |
                   +---------------------------------------------------+
        Authority  | <empty>                                           |
                   +---------------------------------------------------+
        Additional | <empty>                                           |
                   +---------------------------------------------------+

This response is different from the previous one in two ways: the header does not have AA set, and the TTLs are different. The inference is that the data did not come from a zone, but from a cache. The difference between the authoritative TTL and the TTL here is due to aging of the data in a cache. The difference in ordering of the RRs in the answer section is not significant.

Next: 6.2.2. QNAME=SRI-NIC.ARPA, QTYPE=*

Connected: An Internet Encyclopedia
RFC 1034 - 6.2.1. QNAME=SRI-NIC.ARPA, QTYPE=A